Cluster medoid

Note that the centroid is the simple arithmetic mean of the vectors of the cluster members, and this mean is frequently used to represent the cluster as a whole. In situations where a mean is not applicable or appropriate, the median can be used to define the cluster medoid (see Kaufman and Rousseeuw for details). The square-error (also called the within-cluster variance), for a cluster is the sum of squared Euclidean distances to the centroid or medoid for all s items in that cluster ... 

Kmeans Clustering. Type of partitioning cluster analysis in which an object, such as a chemical structure, is placed into one of K clusters, based on how similar the structure is to the average value (or centroid) of each cluster. The average of the cluster may be an actual structure itself, in which case the technique is referred to as K-medoids clustering. 

C. B. Lucasius, A. D. Dane, and G. Kateman, Anal. Chim. Acta, 282, 647 (1993). On k-Medoid Clustering of Large Data Sets with the Aid of a Genetic Algorithm Background, Feasibility and Comparison. 

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